In the handling of small parcels, as, for example, by the United States Postal Service (USPS), it is a standard practice for a human operator to stand amid an array of hampers, illustratively, cloth bags hung from frames, read the addressee information, and throw each individual parcel into a hamper marked for the parcel's destination. The number of hampers in the array is limited to about twenty. More than that would require floor space beyond the reach of a normal person's ability to throw with accuracy. The use of smaller hampers would permit a greater number to be provided within reasonable reach, but would fill up more quickly and have to be replaced more often.
Because there are typically many more destinations than can be accommodated by only twenty hampers, multiple sortings are necessary when using this process, and each parcel must be handled several times before it has found its ultimate destination hamper. Furthermore, the operator must be familiar with the relative position of each destination hamper at each level of the sorting process, in order to maintain even a modicum of efficiency.
The introduction of automation into this field has brought about improvements in the accuracy and speed by which small parcels are sorted and distributed. U.S. Pat. No. 3,759,381, issued Sept. 18, 1973, to M. Mercadie et al., discloses a sorting apparatus in which parcels are loaded into carriers on a moving conveyor system. Each carrier is coded with destination information in an associated memory device, and the memory data is used to cause the carrier to be unloaded at an appropriate one of a plurality of receiving stations. The Mercadie et al. apparatus is relativey complex and requires a large amount of floor space in order to provide access to a useful number of hampers.
U.S. Pat. No. 3,905,896, issued Sept. 16, 1975, to H. L. Jackson et al., discloses a mail sorting and distributing apparatus. The apparatus comprises a multi-tier carousel-like unit that rotates about a vertically-disposed axis. The carousel unit has a number of pigeonholes opening radially outward from a central core; within each pigeonhole is a removable bin. One or more operators, positioned adjacent the continually rotating unit, sort mail by placing it in the appropriate bin as it passes. The bins illustrated in the disclosure are relatively small and thus would appear suited only for flat mail, such as letters and magazines. In order for the Jackon et al. apparatus to handle parcel mail, the bins would have to be larger or they would have to be emptied quite frequently.
The Jackson et al. apparatus is limited in the number of sorting bins which may be used for this purpose. Its number of tiers is limited by the reach of a human operator. Its capacity may be expanded by enlarging the carousel, thereby increasing the number of pigeonholes along its circumference. However, increasing the carousel diameter would extend the operator's average waiting time for a particular pigeonhole to come within reach, assuming a constant velocity at the outer edge of the carousel. There is, therefore, a practical upper limit in the number of storage bins which the Jackson et al. apparatus will accommodate.